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Preliminary Geodynamic Section of Central Italy between 41° and 42° N parallels
No full text""The Central Mediterranean region represents the zone where. the evolution of the Thetian collisional chain appears the most. complex (Bigi et al., 1991; Cavinato et al., 1994; Parotto et al.. 1996; Amato et al. 1997; Cassano et al., 2001; Cassinis at al,. 2003; Billi & Salvini, 2003). In the Central Italian peninsula the. chain is elongated roughly NW-SE and results from the Thetian. suture by the collision between a European and an African. microplate. The sector between the N 41° and N 42° parallels is. one of the most complicate tiles of this puzzle (Salvini, 1993).. Important geodynamic differentiations are present along both. sides (Favali et al, 1993; De Alteriis, 1995).. An ideal E-W transect, from W, locates four main. geodynamic blocks (Fig. 1). To the W is the Sardinia-Corsica. Block of European origin with relics of the sedimentary wedge of. his Thetian margin to the E (Bigi et al, 1991). It follows the. Tyrrhenian Sea, a basin characterized by thinned continental. crust topped with Miocene-Quaternary marine sediments directly. lying on Paleozoic basement (Patacca et al., 1990; Serri et al.,. 2001).. The third block corresponds to the Italian Peninsula with its. Apenninic structures that constitutes the orogen of the chain. (Accordi & Carbone, 1988; Parotto & Praturlon, 2004). The. accretionary prism continues to the E offshore, and it is still. active, in the Adriatic Sea (Patacca & Scandone, 2004). This is. the last block and represents the African margin underthrust to. the chain and it is characterized by a meso-cenozoic carbonate. succession deposited in shallow to open seawaters.. The main accepted geodynamic interpretation states that the. Sardinia block represents a European microplates separated in. Oligocene times (about 38 Ma, Patacca et al., 2008 and ref.. therein). The Apennines is the accretionary prism formed from. the collision in Mio-Pliocene times of the collision between this. microplate and the sedimentary wedge of the Adriatic plate of the. African domain (Adriatic Sea). Many geological evidences still. wait to be properly framed:. i) the substantial lack of the European sedimentary wedge in. the reconstruction of the collision zone;. ii) slices of deep water sedimentary successions associated. with ophiolites, related to the suture zone, outcrop both to the N. and to the S (Southern Apennines);. iii) along the proposed section slices of deep water sediments. has been identified in front of both the westernmost and the. easternmost sides of the chain;. iv) carbonate facies in the Apennines shows in Mesozoic. times deeper waters conditions in the most eastern successions. that is towards the African microplate (Accordi & Carbone,. 1988);. v) in eastern Sardinia a Mesozoic succession of shallow water. limestone outcrop (Tacchi), belongs to the European sedimentary. wedge (Bigi et al., 1991), and shows strong analogies with the. westernmost portions of the Apennine carbonate platforms. (comp. Accordi & Carbone, 1988).. A preliminary, admissible balanced cross sections between. the 41°N and the 42° N parallel has been prepared at the regional. scale by using the layered-HCA method as implemented in the. numerical FORC software (Salvini et al, 2001; Salvini F. &. Storti F., 2004). This section has been compared to the computed. lithosphere flexure of the region as derived from the present. topographic profile.. Results provide the possible framing of the Apennine block. within the African vs European domains, and the location of their. suture zone. Found geometry may represent the basis for a. complete geodynamic study of this complex region."
Erosion by tectonic carving in the Concordia Subglacial Fault Zone, East Antarctica
No full textIn this work we present the analysis of the footwall morphology of the Concordia subglacial extensional fault in the East Antarctic Craton. The Concordia Fault is a regional fault zone that extends for almost 200 km. The displacement, up to 1800 m, and the listric geometry were recognized by numerical modeling of the resulting hangingwall bedrock morphology and is responsible for the marked asymmetry that characterizes the corresponding scarp in the Concordia Subglacial Trench.
The portion of the footwall in the proximity of the master fault exhibits an excavated morphology, about 500 m deep and up to 5 km wide, showing strong correlation with the master fault displacement. We excluded a predominant glacial and fluvial origin of this morphology considering: (i) the sharp topography of the Concordia Fault, suggesting that the fault activity started after the onset of the ice sheet; (ii) the ice-sheet/bedrock contact is characterized by a general negligible erosion/deposition rates still allowing clast removal; (iii) the lack of significant deposits in the Concordia Trench. We hence explored the possibility that this morphology may result from the combined action of fault-induced fracturing and passive clast removal and scattering by flow and plastic deformation within the ice sheet. We introduced the term tectonic carving for this process.
Our modeling shows that tectonic carving relates to the relative fracture intensity in the Concordia fracture zone, that corresponds to the envelope of master and secondary fault damage zones. Fracture intensity depends on the frequency and the displacement of secondary faulting and can be approximated by a normal distribution. Using a Monte Carlo modeling approach we selected the set of parameters that best fits the data set with the carving theoretical curve. The final results of the Monte Carlo analysis show a root mean square of about 50 meters, comparable with the data resolution. This analysis demonstrates a method to unravel the presence of fracture zones in similar, weak erosional environments
The role of fault surface geometry in the evolution of the fault deformation zone: comparing modeling with field example from the Vignanotica normal fault (Gargano, Southern Italy).
No full textFaults have a (brittle) deformation zone that can be described as the presence of two distintive zones: an internal
Fault core (FC) and an external Fault Damage Zone (FDZ).
The FC is characterized by grinding processes that comminute the rock grains to a final grain-size distribution
characterized by the prevalence of smaller grains over larger, represented by high fractal dimensions (up to 3.4).
On the other hand, the FDZ is characterized by a network of fracture sets with characteristic attitudes (i.e. Riedel
cleavages).
This deformation pattern has important consequences on rock permeability. FC often represents hydraulic barriers,
while FDZ, with its fracture connection, represents zones of higher permability.
The observation of faults revealed that dimension and characteristics of FC and FDZ varies both in intensity and
dimensions along them. One of the controlling factor in FC and FDZ development is the fault plane geometry.
By changing its attitude, fault plane geometry locally alter the stress component produced by the fault kinematics
and its combination with the bulk boundary conditions (regional stress field, fluid pressure, rocks rheology) is
responsible for the development of zones of higher and lower fracture intensity with variable extension along the
fault planes.
Furthermore, the displacement along faults provides a cumulative deformation pattern that varies through time.
The modeling of the fault evolution through time (4D modeling) is therefore required to fully describe the
fracturing and therefore permeability.
In this presentation we show a methodology developed to predict distribution of fracture intensity integrating
seismic data and numerical modeling.
Fault geometry is carefully reconstructed by interpolating stick lines from interpreted seismic sections converted
to depth.
The modeling is based on a mixed numerical/analytical method. Fault surface is discretized into cells with their
geometric and rheological characteristics. For each cell, the acting stress and strength are computed by analytical
laws (Coulomb failure). Total brittle deformation for each cell is then computed by cumulating the brittle failure
values along the path of each cell belonging to one side onto the facing one. The brittle failure value is provided
by the DF function, that is the difference between the computed shear and the strength of the cell at each step
along its path by using the Frap in-house developed software. The width of the FC and the FDZ are computed as a
function of the DF distribution and displacement around the fault.
This methodology has been successfully applied to model the brittle deformation pattern of the Vignanotica
normal fault (Gargano, Southern Italy) where fracture intensity is expressed by the dimensionless H/S ratio
representing the ratio between the dimension and the spacing of homologous fracture sets (i.e. group of parallel
fractures that can be ascribed to the same event/stage/stress field)
Alkali-metasomatism and phyllonite development along a major Alpine Shear Zone: the East Tenda Shear Zone (Alpine Corsica, France)
No full textFluid-Rock Interaction During the Schistes Lustrés Nappe Exhumation: an Integrated Structural, Petrological, Fluid Inclusions Study of the Erbalunga Shear Zone (Haute Corse, France)
No full textCombining underactuation with vacuum grasping for improved robotic grippers
No full textThis paper introduces the concept of underactuated vacuum gripper (UVG), which combines two strategies, that is, underactuation and vacuum grasping. The idea is to achieve shape adaptation while improving grip stability by augmenting an underactuated gripper with suction cups. A general theory to predict the contact forces for a UVG is developed and used for comparison reasons with a standard underactuated counterpart. Multibody simulations have been performed to verify the analytical model and quantitatively evaluate the performance of the system in terms of three metrics, namely, grasp stability, contact force distribution, and pull-out force. Finally, the experimental results obtained from a physical prototype of an underactuated linkage-driven gripper equipped with suction cups are illustrated, attesting to the feasibility and potential gain of the system
Introducing POLYPUS: A novel adaptive vacuum gripper
No full textUnderactuated grippers represent an appealing solution that allows complex objects to be grasped and manipulated via passive adaptation of the hand with objects via simple control inputs. The grasping ability can be further improved in combination with vacuum gripping, i.e., by outfitting the gripper phalanges with suction cups, that remains a largely underinvestigated solution. This paper presents a novel gripper, referred to as POLYPUS, that features underactuation and vacuum grasping to handle uneven and even objects made of different materials, including cardboard, glass, sheet metal, and plastic. Being characterized by a solid frame, POLYPUS does not fall in the soft gripper category, while preserving similar adaptability. It provides unique load lifting capacity that ranges from light to heavy objects, whereas most of the existing grippers are tailored for a specific target payload. Being modular in design, POLYPUS can be easily reconfigured for a wide range of object sizes and applications. Results obtained from an extensive set of simulations are included to evaluate the grasping performance expressed in terms of the minimum suction force to handle objects of varying shape, material, and pose
Feedback between fluid flow and rheology during the evolution of the East Tenda Shear Zone (Haute Corse, France).
No full textThe East Tenda Shear Zone (ETSZ) is the major Alpine tectonic boundary marking the overthrusting of the oceanicderived
Schistes Lustrés nappe onto the Hercynian crystalline basement of western Corsica. In this work we present
new structural and geochemical investigations along a transect ranging from the undeformed protolith (PR) to the
contact with the Schistes Lustrés. The results are used to construct a rheological model for the ETSZ.
Shear deformation within the ETSZ is heterogeneously distributed with high-strain domains (shear zones, SZ)
wrapping sigmoid shaped low-strain domains (massive lenses, ML). Locally, mica-rich mylonites occur (phyllonites).
The main foliation is concordant with that in the overlying Schistes Lustrés, strikes NW-SE, and is dominantly
shallow-dipping to NE. The ML mineralogy consists of an assemblage made of quartz, phengite and (relict)
feldspar (epidote, Fe-oxides, zircon and allanite as accessory phases). The SZ mineralogy is invariably dominated
by highly celadonitic (Si4+= 3.5-3.7 a.p.f.u.) phengite (40 ± 10 vol%) and modally abundant quartz (35 ± 5
vol%), albite (15 ± 5 vol%) epidote (<5 vol%) and microcline (10 ± 5 vol%). Locally, Na-amphibole (10-20
vol%) also occurs in the SZ assemblage to form thin (up to 1 m thick) dark mylonitic levels. Stretching lineations
strike WSW-ENE to E-W and consist of quartz-phengite-albite in ML and of Na-amphibole-quartz-albite-phengite
in SZ. Deformation is progressive and evolves from ductile-to-semibrittle conditions. Sense of shear is predominantly
top-to-the-SW and is locally reworked in the phyllonites with top-to-the-NE sense of shear.
Whole rock geochemistry suggests an increasing chemical alteration moving from the undeformed rocks to ML
and SZ. In particular, Ca++ is progressively leached while Na+ and K+ contents systematically increase as deformation
proceeds. Destabilization of Ca-bearing phases, such as plagioclase and epidote, and neoblastesis of
feldspars (albite and microcline) is consistently observed in the more evolved shear zones. These observations
indicate that progressive shear deformation was governed by intensive fluid-rock interaction characterized by increasingly
higher fluid/rock ratios.
The effect of chemical alteration of the host rock by fluids on the rheology of the ETSZ has been estimated taking
into account the modal composition and the fabric of the main lithotypes (PR, ML, SZ, phyllonites). Flow laws
are obtained using an averaging procedure based on weighted averages of single-phase rheology. These flow laws
are used to infer strain rates, construct deformation maps, and estimate the depth of the brittle-ductile transition
for each lithotype during progressive deformation. The combined effects of the feldspar-to-mica reaction and the
development of a strong planar fabric induce weakening and strain localization along the shear zones. Fluid channelling
along these shear zones enhances dominance of Na and K over Ca and, particularly, albite and microcline
neoblastesis. The latter, in turn, generates strain hardening. Among the possible consequences of such feedback
processes between strain localization and fluid-rock interaction are episodes of transient rheology.
The main result of our observations and rheological estimates is that reworking during top-to-the-E regional extension
occurred only in the uppermost part of the deforming crustal section and localized within the weaker
phyllonite levels
Fluid assisted shearing at the depth of the Brittle-Ductile Transition: an integrated structural, petrological, fluid inclusions study of the Erbalunga shear zone, Schistes Lustrés Nappe, Alpine Corsica (France).
No full textSubsurface seepage dynamics and flow types in a Messinian paleoseep system (Maiella Mts., Central Italy)
No full textThe subsurface feeder complexes of mud volcanoes and seepage systems potentially provide valuable information on the evolution of seepage dynamics. Ancient seepage systems in outcrops allow for the observation of expulsion features, which are otherwise commonly beyond seismic resolution. In the Maiella hydrocarbon seep area, the evolution of fluid migration through the sedimentary column during the Messinian Salinity Crisis generated distinctive seep-plumbing features, geological responses, and geochemical signatures in the “Brecciated Limestones” unit. The fluid migration pathways evolved from funnel-shaped feeder channels (Flow-mobilized Sediments) into hydrofractured microbial carbonate buildups (Limestone Buildups), and finally into blow-out micropipes in the host sediment (Patchy Limestones), as overpressure dissipated through the plumbing system. The Flow-mobilized Sediments (δ13C down to − 24.5‰ PDB-1) correspond to the highest flow rates in the whole area, whereas the Patchy Limestones (δ13C down to − 39.3‰ PDB-1) correspond to the slowest flow rates within the intrusive zone. The Limestone Buildups show different degrees of hydrofracturing that reflect different flow rates (δ13C down to − 27.5‰ PDB-1). The fluid transport mechanisms evolved from focused venting through neoformed feeder channels, where sediments elutriated from depths were carried out (the sediment-prone response to fluid migration), to high-rate seepage triggering high hydrofracturation in the microbial buildups. While the hydrocarbon-rich fluids contemporaneously triggered authigenic precipitation (the mineral-prone response to fluid migration), progressive upward and lateral flow deceleration resulted in gradually weaker hydrofracturing of the microbial buildups and finally only local cementation in the form of carbonate patches within the host sediments
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